Salivary secretions contain two distinct mucins, a high molecular weight mucin named MG1 and a low molecular weight mucin named MG2. Mucins protect oral surfaces against desiccation, form a selectively permeable diffusion barrier between underlying surfaces and the external environment, lubricate hard and soft tissues to minimize mechanical injury, facilitate speech and swallowing and provide a physical barrier to protect against colonization of potentially harmful microbes and viruses. We have shown that MG1 is actually a mixture of mucin gene products, containing MUC4, MUC5B and a novel salivary mucin (NSM), whereas MG2 is a single gene product encoded in the MUC7 gene. MG1 and MG2 are differentially expressed in major and minor salivary glands and the overall goal of this project is to understand their structural features and functional properties. The specific aims of this project are to: 1. determine the structural organization and sequence of mucin gene products comprising MG1 by characterization of a novel salivary mucin (NSM) and elucidating the C-terminal sequence of MUC4. 2. investigate the biosynthesis and assembly of MUC4, MUC5B and NSM using mucin constructs expressed in COS-7 cells. 3. evaluate interactions of MG2 with oral microbes and investigate MG2 heterotypic complexes with other salivary proteins in the yeast two hybrid system. 4. study expression of trefoil peptides in major and minor salivary glands using immunohistochemistry and in situ hybridization. 5. examine MG1 and MG2 levels in salivary secretions and whole saliva and determine secretion profiles using mucin-specific capture ELISAs.